1. Field of the Invention
The present invention relates in general to a reversible heat sensitive recording material, and in more particular to such a composition composed of an ester compound having a specific .DELTA.T value (.DELTA.T in centrigrade degree=melting point-clounding point) and capable of developing upon the application of partial heat of low or high temperature. The image thus developed in normal or reversed form can be maintained for recording in a condition of specific temperature ranges, and can be erased by exposure to a low or high temperature. Thus, this invention can be applied to cases where the marking or recording requires repeated erasure.
2. Description of the Prior Art
Conventional reversible heat sensitive recording materials in general utilize the thermal sensitive coupling properties of metallic complex salts such as Ag.sub.2 HgI.sub.4 and Cu.sub.2 HgI.sub.4. However, these materials have the following disadvantages:
(1) Impracticable in optionally selecting an image maintaining temperature
The metallic complex salts are limited in the kind of available compound and require 40.degree. C. or higher to maintain their recording phase. Consequently, these materials are not acceptable where the recording must be kept at room temperature or lower.
(2) Narrower recording temperature range for maintaining the recording
Since the temperature range in which the contained metallic complex salt maintains its recording phase is extremely narrow, strict temperature control is required to keep the marking or recording visible.
(3) Improper contrast of the recording against the background
Since the obtainable color strength is not sufficient, the image or recording is not clearly visible against the background.
(4) Unavailable freely selecting a hue
(5) Various limitations on preparating and processing dye
Because of these problems, most conventional reversible heat sensitive recording materials are widely unacceptable in the practical fields of applications.